Polymers, condensation

Condensation polymers are formed from two monomers containing two functional groups. The formation of a bond usually leads to the elimination of a simple by-product (such as water), and this occurs in discrete steps (i.e. not via a chain reaction). The polymer is usually composed of an alternating sequence of the two monomers. 

Polyamides (or nylons) are produced from heating dicarboxylic acids with diamines. The amine acts as the nucleophile and reacts with the carboxylic acid in a nucleophilic acyl substitution reaction (see Section 9.3). 

Polyesters are produced from heating dicarboxylic acids (or diesters) with Reactions of esters are discussed in diols. Section 9.7 

Polyurethanes are produced from reaction of diols with diisocyanates. Nude- isocyanate has the formula 

In a proton transfer, H moves from one part of the molecule to another 

Condensation polymers are those produced by a reaction of the type 

The number of monomeric units is always one unit larger than the number of segments. If x is large, the difference is negligible. 

The probability that the functional group of the first unit has reacted is equal to p, for the second unit it is equal to p, for the third unit it is equal to p, and so on. For the X 1 unit the probability is p that the molecule contains at least x — 1 reactive groups, or at least x units. The probability that the xth unit has not reacted is 1 - p. That is, the probability for the last (xth) unit to be terminated is 1 — p. Then the probability that among the x monomeric units x — 1 units have reacted and one (the end unit) has not reacted is 

If No is the total number of monomers (e.g., OH—R—COOH units) and N is the total number of macromolecules, then the total number of x-mers is 

If w is the mass of a monomer unit, then the total mass of No monomers is A oi -The mass of one x-mer is xw the mass of Nx x-mers is Nxxw. We now have the ratio 

Condensation polymers are formed from the reaction of two different bifunctional monomers A and B which form AB by the reaction with the elimination of a product, usually water 

the polymer grows at both ends by condensing and stops when at least one of the reagents is fully consumed. Nylon 66 is a condensation polymer between a 6-carbon diamine and 6-carbon dicarboxylic acid. 

Linear condensation polymers are produced when the constituent monomers contain two functional groups each. When a single monomer is polymerized, the product is made of chains whose repeat unit corresponds to the monomer. An example of this type is nylon 6, the structure of which is shown in Fig. 1.10. If two different monomers are polymerized, the result most often is a chain whose repeat unit corresponds to the two different monomers arranged alternately. An example of this type is nylon 66, the structure of which is shown in 

In each step of the synthesis of a condensation pofymer a small molecule, usually water, is split off. For example, the reaction of hexametlqrlene diamine 

Note that these condensation polymers are of the form 

This absolute regularity in the order of placement of the monomers enhances the tendency of the molecule to form crystals when cooled from the liquid state this molecular characteristic is consequently of the greatest mechanical signifrcance, as will be shown repeatedly in the following chapters. 

Copolymers are polymers composed of two or more different monomers. For example, if ethylene and propylene are polymerized simultaneously then the polymer will contain both ethylene and propylene units. If the mixture of gaseous monomers is mainly ethylene, then the copolymer will consist of linear ethylene sequences with, here and there, a propylene unit. (Conversely, the polymerization of propylene with a small amount of ethylene produces linear sequences of polypropylene separated here and there by an ethylene unit. The reader will anticipate that the first copolymer will exhibit the properties of a modified polyethylene, the second of a modlHed polypropylene, and this is in fact the observed behaviour. 

The combination of monomers to form copolymers can be compared with the mixing of metals to form solid solutions, which is the basis of all  

The first synthetic fiber, nylon 66, is a condensation copolymer of two molecules one with carboxy groups at each end (adipic acid) and one with amine groups at both ends (hexamethylenediamine)  

Water pipes, garden hoses, plastic wrap 

Nylon was first made by Wallace Carothers at DuPont in 1931. The versatility of nylons is so great that the annual production of itylons and related substances now amounts to several billion pounds. 

Many polymers with enhanced heat stability can be prepared simply by direct condensation. These aromatic polymers often contain a heterocyclic unit. The materials are high melting, somewhat infusible, and usually low in solubility. Many aromatic polyimides belong here. Polyimides, as a separate class of polymers, were discussed in an earlier section, because many are common commercial niaterials. On the other hand, the materials described in this section might be considered special and, perhaps, at this point, still too high priced for common usage. 

Many polybenzimidazoles are prepared by direct condensation. They are colored polymers that mostly melt above 400 One such material is formed from 3,3 -diaminobenzidine and dipheyl isophthalate by heating the two together at 350-400 °C in an inert atmosphere  

All of the above materials maintain useful properties up to 300 °C in air and can be fabricated into fibers. 

Some polymeric materials are completely free from hydrogens. An example is polysulfodia-zole a lyimide prepared from pyrazine-l,2,4,5-tetracarboxylic acid anhydride and diami-nothiazine.  

Films from this polysulfodiazole maintain their strength and stability at 592 °C. Preparation of several other, similar polyimides was reported. Apolyimide, however, prepared from diaminothia-zole with pyromellitic dianhydride chars at 320 °C in air. The chemistry and preparations of the principal types of polyheteroarylenes were reviewed by Krongauz.  

29 Given the structural diagrams of a dicarboxylic acid and a dialcohol, predict the structural diagram of the product condensation polymer given the structural diagram of a condensation polymer, predict the structural diagrams of the dicarboxylic acid and dialcohol from which it can be formed. 

Co to http //now.brookscole.com/ cracolice5e and click Chemistry Interactive for the module Polyester Formation. 

In Section 21.12 you learned that carboxylic acids react with alcohols to form esters and with ammonia and amines to form amides. In each reaction, a molecule of water is split out in a condensation reaction. Polymer chemists use these same reactions to form polyesters and polyamides. However, to form the polymer chain by repeated condensation reactions, you must use a t/tcarboxylic acid (two carboxyl groups), such as terephthalic acid, and a t/talcohol (two hydroxyl groups), such as ethylene glycol, as shown here. 

The linear polyester formed above is a polyethylene terephthalate, or PET. It has a molar mass of about 15,000 g/mol. Because the ester group is polar, attractions between polymer chains are of a dipole type and are fairly strong. As a result, PET polymers are used in fibers such as Fortrel and Dacron (Fig. 21.35). Longer PET polymers are used for tire cords. Made into a Mylar film and coated with magnetic particles, PET becomes the base for audio and video recording tape. Two-liter soft drink bottles are a PET polymer. 

The two compounds react at the interface between the two layers to form nylon 66... 

Metallocene methylene polymers have also been prepared via the preparation of an a-metallocenylcarbocation with an acidic or Lewis acid initiator, followed by polycondensation involving electrophilic substitution of the metallocene nucleus 

The monomers 26 and 27 have also been used to synthesize segmented poly (ether urethane) from poly(propylene glycol) (PPG) and 4,4 -methylene-bis(phenyliso-cyanate) (MDI) [37]. In the prepolymer method employed, MDI (2 equiv.) and PPG (1 equiv.) were allowed to react at 60 °C in the presence of 1 mol% dibutyltin 

Monomer (Ml) Monomer (M2) Process (base used) yield, % 7 dL/g 

There have been reports of the synthesis of organometallic arylidene polyesters containing ferrocene derivatives in the main chain. Interfacial polymerization of 

The Mn of these polymers, determined by end group analysis using NMR spectral data, was 3270 — 4550. These polymers were suggested to have improved thermal stability and flame resistance. 

In all the preceding polymerization methods we have seen how to utilize the double bond in an unsaturated organic compoimd to link many molecules together into a polymeric chain. Also, in all of these processes the polymer was produced starting from a single monomer. In contrast in this section we will look at polymers that are prepared from the reaction of two difunctional monomers with each other. In all the polymerization reactions that we have seen so far there was no side-product formation. For example, ethylene was converted into polyethylene acrylonitrile was converted into polyacrylonitrile and so on. During this conversion the entire stmc-tural unit of the monomer was incorporated into the polymer without any side-product formation. However, in the preparation of condensation polymers a small molecule (such as water or methanol) is eliminated as the side-product. Another important difference is that condensation polymerization is usually a step-growth polymerization. This means that the polymerization proceeds in a series of steps. To make this point clear let us recall the polymerization of ethylene by the free-radical method. In the free-radical process the polymerization of various chains are initiated by the 

The number 66 refers to the fact that there are SIX C atoms in each monomer. Other nylons, such as nylon 610, are made from various combinations of molecules similar to adipic acid and hexamethylenediamine. 

In a similar way we can form ethers, amides, urethanes, ureas, suMbnes and others. 

There are several important points to note in the formation of polymers by a 

Examples of the types of chemical functions which can be used to produce 

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Polymers can be classified as addition polymers and condensation polymers. Addition polymers are formed by iiitermolecular reactions of the monomeric units without the elimination of atoms or groups. An example is vinyl chloride, which can be made to combine with itself to yield polyvinyl chloride ... 

ETHYLENE We discussed ethylene production in an earlier boxed essay (Section 5 1) where it was pointed out that the output of the U S petrochemi cal industry exceeds 5 x 10 ° Ib/year Approximately 90% of this material is used for the preparation of four compounds (polyethylene ethylene oxide vinyl chloride and styrene) with polymerization to poly ethylene accounting for half the total Both vinyl chloride and styrene are polymerized to give poly(vinyl chloride) and polystyrene respectively (see Table 6 5) Ethylene oxide is a starting material for the preparation of ethylene glycol for use as an an tifreeze in automobile radiators and in the produc tion of polyester fibers (see the boxed essay Condensation Polymers Polyamides and Polyesters in Chapter 20)... 

The leader of DuPont s effort was Wallace H Carothers who reasoned that he could reproduce the properties of silk by constructing a polymer chain held together as is silk by amide bonds The neces sary amide bonds were formed by heating a dicar boxylic acid with a diamine Hexanedioic acid adipic acid) and 1 6 hexanediamme hexamethylenedi-amine) react to give a salt that when heated gives a polyamide called nylon 66 The amide bonds form by a condensation reaction and nylon 66 is an example of a condensation polymer... 

Polyesters are a second class of condensation polymers and the principles behind their synthesis parallel those of polyamides Ester formation between the functional groups of a dicarboxylic acid and a diol... 

Condensation polymer (Section 20 17) Polymer m which the bonds that connect the monomers are formed by condensa tion reactions Typical condensation polymers include poly esters and polyamides... 

Poly(amide-imide) is the condensation polymer of 1,2,4-benzenetricarboxylic anhydride and various aromatic diamines and has the general structure ... 

In the last section we examined some of the categories into which polymers can be classified. Various aspects of molecular structure were used as the basis for classification in that section. Next we shall consider the chemical reactions that produce the molecules as a basis for classification. The objective of this discussion is simply to provide some orientation and to introduce some typical polymers. For this purpose a number of polymers may be classified as either addition or condensation polymers. Each of these classes of polymers are discussed in detail in Part II of this book, specifically Chaps. 5 and 6 for condensation and addition, respectively. Even though these categories are based on the reactions which produce the polymers, it should not be inferred that only two types of polymerization reactions exist. We have to start somewhere, and these two important categories are the usual place to begin. 

Condensation polymers such as polyesters and polyamides are especially well suited to this method of molecular weight determination. For one thing, the molecular weight of these polymers is usually less than for addition polymers. Even more pertinent to the method is the fact that the chain ends in these molecules consist of unreacted functional groups. Using polyamides as an example, we can readily account for the following possibilities ... 

Comparable but equally specific considerations must be applied to other condensation polymer systems. The following example is an illustration of the application of these ideas to the molecular weight of polyamides. 

Condensation polymers prepared with some monomer of functionality greater than 2, for example, a polyester formed with some glycerol or tricarboxylic acid. 

It is the third of these criteria that offers the most powerful insight into the nature of the polymerization process for this important class of materials. We shall frequently use the terms step-growth and condensation polymers as synonyms, although by the end of the chapter it will be apparent that step-growth polymerization encompasses a wider range of reactions and products than either criteria (1) or (2) above would indicate. 

To see why the assumption of equal reactivity is so important to step-growth polymers, recall from Table 1.2 the kind of chemical reactions which produce typical condensation polymers ... 

Howardt describes a model system used to test the molecular weight distribution of a condensation polymer The polymer sample was an acetic acid-stabilized equilibrium nylon-6,6. Analysis showed it to have the following end group composition (in equivalents per 10 g) acetyl = 28.9,... 

This change of notation now expresses Eq. (6.65) in exactly the same form as its equivalent in Sec. 5.4. Several similarities and differences should be noted in order to take full advantage of the parallel between this result and the corresponding material for condensation polymers from Chap. 5 ... 

Uses. The largest uses of butanediol are internal consumption in manufacture of tetrahydrofuran and butyrolactone (145). The largest merchant uses are for poly(butylene terephthalate) resins (see Polyesters,thermoplastic) and in polyurethanes, both as a chain extender and as an ingredient in a hydroxyl-terminated polyester used as a macroglycol. Butanediol is also used as a solvent, as a monomer for vadous condensation polymers, and as an intermediate in the manufacture of other chemicals. 

A series of compounded flame retardants, based on finely divided insoluble ammonium polyphosphate together with char-forming nitrogenous resins, has been developed for thermoplastics (52—58). These compounds are particularly useful as iatumescent flame-retardant additives for polyolefins, ethylene—vinyl acetate, and urethane elastomers (qv). The char-forming resin can be, for example, an ethyleneurea—formaldehyde condensation polymer, a hydroxyethylisocyanurate, or a piperazine—triazine resin. 

Phosphorus-Containing Polymers. A large number of addition and condensation polymers having phosphoms built in have been described, but few have been commercialized (131,132). No general statement seems warranted regarding the efficacy of built-in vs additive phosphoms (133). However, in textile fibers, there is greater assurance of permanency. 

PoIya.mines are condensation polymers containing nitrogen they are made by a variety of synthetic routes. Most of the commercial polyamines are made by reaction of epichlorohydrin with amines such as methylamine [25988-97-0] or dimethylamine [39660-17-8] (18,19). Branching can be increased by a dding small amounts of diamines such as ethylenediamine [42751-79-1]. A typical stmcture of this type of polyamine is stmcture (9). 

Chemical Stabilization Processes. This method is more versatile and thus has been used successfully for more materials than the physical stabilization process. Chemical stabilization is more adaptable for condensation polymers than for vinyl polymers because of the fast yet controUable curing reactions and the absence of atmospheric inhibition. 

Aromatic Isocyanates. In North America, aromatic isocyanates ate heavily used as monomers for addition and condensation polymers. The principal appflcafions include both flexible and rigid polyurethane foam and nonceUulat appflcations, such as coatings, adhesives, elastomers, and fibers. 

Uses. Pyromellitic dianhydride imparts heat stabUity in applications where it is used. Its relatively high price limits its use to these applications. The principal commercial use is as a raw material for polyimide resins (see POLYIMIDES). These polypyromellitimides are condensation polymers of the dianhydride and aromatic diamines such as 4, -oxydianifine ... 

The packaging (qv) requirements for shipping and storage of thermoplastic resins depend on the moisture that can be absorbed by the resin and its effect when the material is heated to processing temperatures. Excess moisture may result in undesirable degradation during melt processing and inferior properties. Condensation polymers such as nylons and polyesters need to be specially predried to very low moisture levels (3,4), ie, less than 0.2% for nylon-6,6 and as low as 0.005% for poly(ethylene terephthalate) which hydrolyzes faster. 

P. W. Morgan, Condensation Polymers by Interfacial and Solution Methods olm. Wiley Sons, Inc., New York, 1965. 

The two complementary functional groups that react to form condensation polymers may also occur in a single monomer, eg, a hydroxy acid,... 

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